for National Geographic News
The depth of human tragedy resulting from the Indian Ocean tsunami disaster is incalculable, even though the scale of visible devastation to coastal towns is now shockingly clear.
But what of marine life? When the tsunami struck, land and ocean merged in a most terrifying way. People and uprooted trees were carried out to sea, while stingrays and sharks were left stranded in fields and parking lots.
The impacts are difficult to gauge. Scientists and conservationists say the future of coastal towns will be closely intertwined with that of fragile marine ecosystems. If coral reefs and mangroves aren't nursed and protected, they say, many human livelihoods will be hard to revive.
The most obvious marine casualties of the tsunami waves were washed up in their wake. In Thailand, for instance, dolphins were swept 500 yards (500 meters) inland. Many dead and injured sea turtles were left high and dry, and a three-foot (one-meter) shark ended up in a hotel swimming pool. Beaches were littered with dead fish as well as human bodies.
And while there are fears for some marine speciessuch as threatened dugongs and saltwater crocodiles in the Andaman Islandsscientists are most concerned about the habitats these animals depend on.
While it says the overwhelming priority remains the human relief effort, the United Nations Environment Programme (UNEP) has begun to assess environmental damage caused by the tsunami triggered by the massive earthquake off northern Sumatra on December 26.
Early reports indicate that many coral reefs have been extensively damaged, according to Stefan Hain, head of the Coral Reef Unit at UNEP's World Conservation Monitoring Centre in Cambridge, England.
Researchers are particularly worried about the backwash of mud and other debris as the tsunami waves receded. "We have satellite images of regions such as the Andaman and Nicobar Islands which show that a huge amount of sediment and debris has been washed from the land and back into the sea," Hain said.
Hain said experts are working to determine whether these "turbidity clouds" could smother affected coral reefs.
Coral reefs are highly diverse, complex communities. Reefs are built by coral polyps and symbiotic algae, which need pristine waters to thrive.
"The algae depend on sunlight and, via the algae, so do the corals," Hain added. "If you deprive them of sunlight, it is very difficult for corals to survive. To a certain extent, corals have self-cleaning mechanisms, but we will just have to see whether they will cope with this amount of debris."
SOURCES AND RELATED WEB SITES